Major Soil Types Research Articles

Vegetation structure and composition in the semi-arid Mapungubwe Cultural Landscape

235 ABSTRACT: Mapungubwe Cultural Landscape (MCL) woody vegetation was characterized to establish structural and compositional attributes. Stratified random sampling based on major soil types was used and nine plant variables were measured in 137(20x30) m 2 sampling plots; these being genera, species and family names; basal circumference; plant height; depth and diameter of tree canopy; number of stems per plant; plant life status; number of trees and shrubs; and number of saplings. A total of 3114 woody plants were sampled, comprising an assemblage of 28 families, 63 genera and 106 species. The results suggest alluvial floodplain flanking the Limpopo River is a biodiversity hotspot with high plant species diversity (H �=1.8-2.2) 1/ha, taller trees (P<0.05) with median height per plot ranging between 6.1-10 m, high canopy volume at 105783 (443155m 3 /ha) and basal area (16.9-111m 2 /ha). The Arenosols-Regosol stratum had significantly shorter trees (P<0.05) with median height per plot between 3-4 m, low species diversity (H �=0.8-2.3) 1/ha, low basal area (3.23-48.2m 2 /ha) and low canopy volume (6687.08(155965.00) m 3 /ha. The Cambisol- Luvisol stratum in the western section of MCL had high number of stems/plant at 1.65 (1.40), high woody plant density 483.33 (900.00) 1/ha, F 3,137 =19.07,P<0.05), high density of dead plants 16.67 (133.30) 1/ha and high sapling density 208.33 (850.00) 1/ha. The present study suggests soil type is a key determinant of woody vegetation structure and composition. The study recommends regular vegetation monitoring, periodic update of plant species inventories in protected areas, control of exotic invasive woody plant species found along the Limpopo river floodplain within the biodiversity management framework of Greater Mapungubwe Transfrontier Conservation Area initiative.

Yield gap analysis of rainfed wheat demonstrates local to global relevance

SUMMARYAustralia has a role to play in future global food security as it contributes 0·12 of global wheat exports. How much more can it contribute with current technology and varieties? The present paper seeks to quantify the gap between water-limited yield potential (Yw) and farmer yields (Ya) for wheat in Australia by implementing a new protocol developed by the Global Yield Gap and Water Productivity Atlas (GYGA) project. Results of past Australian yield gap studies are difficult to compare with studies in other countries because they were conducted using a variety of methods and at a range of scales. The GYGA project protocols were designed to facilitate comparisons among countries through the application of a consistent yet flexible methodology. This is the first implementation of GYGA protocols in a country with the high spatial and temporal climatic variability that exists in Australia.The present paper describes the application of the GYGA protocol to the whole Australian grain zone to derive estimates of rainfed wheat yield gap. The Australian grain zone was partitioned into six key agro-climatic zones (CZs) defined by the GYGA Extrapolation Domain (GYGA-ED) zonation scheme. A total of 22 Reference Weather Stations (RWS) were selected, distributed among the CZs to represent the entire Australian grain zone. The Agricultural Production Systems sIMulator (APSIM) Wheat crop model was used to simulate Yw of wheat crops for major soil types at each RWS from 1996 to 2010. Wheat varieties, agronomy and distribution of wheat cropping were held constant over the 15-year period. Locally representative dominant soils were selected for each RWS and generic sowing rules were specified based on local expertise. Actual yield (Ya) data were sourced from national agricultural data sets. To upscale Ya and Yw values from RWS to CZs and then to national scale, values were weighted according to the area of winter cereal cropping within RWS buffer zones. The national yield gap (Yg = Yw–Ya) and relative yield (Y% = 100 × Ya/Yw) were then calculated from the weighted values.The present study found that the national Yg was 2·0 tonnes (t)/ha and Y% was 47%. The analysis was extended to consider factors contributing to the yield gap. It was revealed that the RWS 15-year average Ya and Yw were strongly correlated (R2 = 0·76) and that RWS with higher Yw had higher Yg. Despite variable seasonal conditions, Y% was relatively stable over the 15 years. For the 22 RWS, average Yg correlated positively and strongly with average annual rainfall amount, but surprisingly it correlated poorly with RWS rainfall variability. Similarly, Y% correlated negatively but less strongly (R2 = 0·33) with RWS average annual rainfall, and correlated poorly with RWS rainfall variability, which raises questions about how Australian farmers manage climate risk. Interestingly a negative relationship was found between Yg and variability of Yw for the 22 RWS (R2 = 0·66), and a positive relationship between Y% and Yw variability (R2 = 0·23), which suggests that farmers in lower yielding, more variable sites are achieving yields closer to Yw. The Yg estimates appear to be quite robust in the context of estimates from other Australian studies, adding confidence to the validity of the GYGA protocol. Closing the national yield gap so that Ya is 0·80 of Yw, which is the level of Yg closure achieved consistently by the most progressive Australian farmers, would increase the average annual wheat production (20·9 million t in 1996/07 to 2010/11) by an estimated 15·3 million t, which is a 72% increase. This indicates substantial potential for Australia to increase wheat production on existing farmland areas using currently available crop varieties and farming practices and thus make a substantial contribution to achieving future global food security.

An application of Embedded Markov chain for soil sequences: Case study in North Western part of Algeria

Embedded Markov chain (EMC) has long history in geological domains, particularly to define the most representative sequences from statigraphic logs. In other words, what is viewed as a meaningless and disordered stratigraphic layer stack can be reorganized in a meaningful sequence by using EMC. This method was transposed in this paper to obtain soil sequences from data retrieved from soil map made by authors, covering a part of the region of Traras (N.W. of Algeria) and containing 13 major soil types. Each major soil type occupies at least one polygon in the map and allow to establish soil adjacencies, which have been tabulated in a matrix regardless to the direction. Three EMC methods have been tested, Walker, Harper and Turk using Strati-signal software and to erect soil relationship diagrams (SRD) representing the most significant links between soils. Significant test is the main difference between the above mentioned three EMC methods. It has been shown that Harper method is quite insensitive to small number of transitions. Besides, all three methods agreed for one soil sequence made by four soils: lithics leptosols- cambisols chormics- cambisols calcarics- fluvisols representing theoretical catena the most representative to the study area. This soil sequence is relevant to the study region and even to the whole Mediterranean region, and is commanded by the topography and the Mediterranean bioclimate. Walker SRD is the most realistic but the most difficult to interpret because of the high number of soil links, Harper SRD gives interesting results. Although the results didn’t bring something new to the soil interpretation and soil pedogensis but EMC applied to a finer scale may highlights other hidden relationships between soils.

Effect of phosphorus management in rice–mungbean rotations on sandy soils of Cambodia

AbstractNitrogen (N) and phosphorus (P) deficiencies are key constraints in rainfed lowland rice (Oryza sativa L.) production systems of Cambodia. Only small amounts of mineral N and P or of organic amendment are annually applied to a single crop of rainfed lowland rice by smallholder farmers. The integration of leguminous crops in the pre‐rice cropping niche can contribute to diversify the production, supply of C and N, and contribute to soil fertility improvement for the subsequent crop of rice. However, the performance of leguminous crops is restricted even more than that of rice by low available soil P. An alternative strategy involves the application of mineral P that is destined to the rice crop already to the legume. This P supply is likely to stimulate legume growth and biological N2 fixation, thus enhancing C and N inputs and recycling N and P upon legume residue incorporation. Rotation experiments were conducted in farmers' fields in 2013–2014 to assess the effects of P management on biomass accumulation and N2 fixation (δ15N) by mungbean (Vigna radiata L.) and possible carry‐over effects on rice in two contrasting representative soils (highly infertile and moderately fertile sandy Fluvisol). In the traditional system (no legume), unamended lowland rice (no N, + 10 kg P ha−1) yielded 2.8 and 4.0 t ha−1, which increased to 3.5 and 4.7 t ha−1 with the application of 25 kg ha−1 of urea‐N in the infertile and the moderately fertile soil, respectively. The integration of mungbean as a green manure contributed up to 9 kg of biologically fixed N (17% Nfda), increasing rice yields only moderately to 3.5–4.6 t ha−1. However, applying P to mungbean stimulated legume growth and enhanced the BNF contribution up to 21 kg N ha−1 (36% Nfda). Rice yields resulting from legume residue incorporation (“green manure use”–all residues returned and “grain legume use”–only stover returned) increased to 4.2 and 4.9 t ha−1 in the infertile and moderately fertile soil, respectively. The “forage legume use” (all above‐ground residues removed) provided no yield effect. In general, legume residue incorporation was more beneficial in the infertile than in the moderately fertile soil. We conclude that the inclusion of mungbean into the prevailing low‐input rainfed production systems of Cambodia can increase rice yield, provided that small amounts of P are applied to the legume. Differences in the attributes of the two major soil types in the region require a site‐specific targeting of the suggested legume and P management strategies, with largest benefits likely to accrue on infertile soils.

Natural Chemical Degradation of Soils in the Indian Semi-Arid Tropics and Remedial Measures

Most published research on soil degradation in general emphasizes the role of anthropogenic factors. Even among the natural soil degradation processes the regressive pedogenic processes that lead to the formation of CaCO3 and concomitant development of subsoil sodicity and the adverse effects of palygorskite on the soils of the semi-arid tropics (SAT), have received little global attention as the natural processes of chemical degradation of soils. Studies in India during the last two decades, however, have demonstrated the important role of regressive pedogenic processes in natural degradation of major soil types in the Indian SAT regions. The present article summarizes the research on natural degradation of soils in the Indian SAT. The management practices to reclaim the degraded soils are also discussed with examples.

Integrated remote sensing and GIS‐based approach for deciphering groundwater potential zones in the central region of Saudi Arabia

The scarcity of fresh water resources is a major challenge facing Saudi Arabia. Groundwater is the major conventional water source in Saudi Arabia. Therefore, it is important to identify areas having groundwater potential; however, the current methods of groundwater exploration consume a lot of time and money. Alternatively, this paper introduces a methodology to identify groundwater potential zones in the Central part of Saudi Arabia using remote sensing and GIS‐based decision support system (DSS) and fuzzy logic based spatial model. The DSS model generated suitability maps for groundwater potential (GWP) zones with five suitability classes, i.e. excellent, very good, good, poor, and very poor based on the integration of nine thematic maps: soil type, land cover and land use, slope, lithology, rainfall, geological structure, geomorphology, lineament density, and drainage density using a hierarchical process analysis (AHP). The spatial distribution of the GWP zones by AHP-DSS and fuzzy logic model showed that ‘excellent’ suitable areas for GWP were concentrated in the main wadi channels within the central, northeastern and southeastern parts of the study area. The AHP-DSS model showed that 1.47 % (5608.5 km2) and 4.15 % (15,787.3 km2) of the study area was classified as excellent and very good, respectively, while 12.59 % (47,911.1 km2), 74.82 % (284,670.9 km2) and 6.97 % (26,519.9 km2) of the area were classified as good, poor and very poor, respectively. On the other hand, integrating thematic layers using fuzzy logics indicates that 2.8 % (10,739 km2), 8.8 % (33,587 km2), 7.9 % (30,106 km2), 60 % (228,361 km2), and 20.4 % (77,705 km2) of the entire study area is considered as excellent, very good, good, poor, and very poor areas for groundwater potential, respectively. The majority of the areas with excellent to very good suitability had slopes between 0 and 3 % and were in intensively cultivated fields. The major soil type in the excellent to very good zones was Arenosols and Lithosols. The rainfall ranged from 125 to 226 mm/year, while the main lithological structures are alluvial deposits, carbonate rocks, and mixed sedimentary consolidated rocks. These areas are mainly located in the carbonate–sulfate formations, which extend from the Lower Jurassic to the Lower Cretaceous and the sandstone aquifers. Moreover, they have lineament density ranged from 4.75 to 8.34 km/km2, and drainage density ranged from 1 to 1.83 km/km2. Furthermore, the study revealed that lineament density is closely related to groundwater occurrence and yield and is essential to groundwater surveys, development, and management. Validation of the two models employed depends on comparing existing groundwater well locations with the suitability map generated using the proximity analysis tools of ArcGIS 10.2. The results obtained from AHP-DSS approach and fuzzy model were verified with field survey and were found to be in very good and good agreement, respectively. The validation results showed that the database and methodology used for developing the suitability model for GWP zones, including the suitability levels of the criteria and the criteria’s relative importance weights, to have yielded accurate results.

Investigating the source of radiocesium contaminated sediment in two Fukushima coastal catchments with sediment tracing techniques

The Fukushima Dai-ichi nuclear power plant accident resulted in the fallout of significant quantities of radiocesium. After deposition on the soil surface, rainfall and spring flood events transfer radiocesium downstream. Identifying the source of contaminated sediment is important for managing potential downstream radiocesium contamination. Soil (n = 37) and sediment (n = 211) were sampled from November 2011 to May 2014 in the Mano and the Niida coastal catchments. Two sediment fingerprinting approaches quantified the source of radiocesium contaminated sediment. First, cesium-137 activities in surface soil and sediment samples were modelled to determine the contribution of upstream, more contaminated areas, to sediment transiting the more densely populated coastal plain. Second, elemental geochemistry of three major soil types (zs, Cambisols and Fluvisols) was used to model the relative contribution of these soils to sediment sampled throughout the catchments. In the Niida catchment, 47% (σ 19%) of sediment sampled in the coastal plain was modelled to be derived from the upstream area whereas, it was only 19% (σ 19%) in the Mano catchment. The main factor driving this difference is the presence of a large dam on the main stem of the Mano River. Geochemical modelling results indicated that Fluvisols, an alluvial soil type on which paddy fields are typically cultivated, supply the majority of sediment (μ 76, σ 14%). The results confirm that the management of dams is fundamental to radiocesium migration. Moreover, this research indicates that Fluvisols and concomitantly, rice paddies on this soil type, supply a disproportionate amount of sediment. Managing sediment derived from Fluvisols, while incorporating potential impacts from major dams, should help mitigate the downstream migration of radiocesium contaminated sediment.

Near Infrared Spectra and Soft Independent Modelling of Class Analogy for Discrimination of Chernozems, Luvisols and Vertisols

The objective of the present study was to use near infrared diffuse reflectance spectroscopy and chemometrics to distinguish three major soil types in Bulgaria – Chernozems, Luvisols and Vertisols. The diffuse reflectance spectra of 78 air-dried and sieved soil samples collected from grasslands and arable agricultural lands and classified as Chernozems, Luvisols and Vertisols were obtained in the spectral range 700–2500 nm. Second-derivative transformation of soil and clay spectra was performed in order to find soil spectral differences based on the clay minerals content. Soft independent modelling of class analogy (SIMCA) was performed to classify samples according to their classes. Results show that the samples can be distinguished according to their classes as the SIMCA models correctly classified 100% of the samples in both calibration and validation sets. According to the discrimination power parameter of the SIMCA procedure, the most important wavelengths in the classification models of Chernozem, Luvisol and Vertisol soils were related to the content of clay minerals such as kaolinite and montmorillonite, smectite minerals, organic matter and carbonates.

Soil phosphorus status and environmental risk of phosphorus run-off from pastures in south-eastern New South Wales

Soils were sampled from 136 sites representing the major soil types in the Sydney drinking water catchments to provide an overview of agronomic phosphorus requirement and phosphorus environmental risk for the various pastoral land uses, which together comprise 40% of the 15700-km2 catchment area. Critical values for Colwell P (estimated from the phosphorus buffering index) were subtracted from the measured Colwell P to derive a ‘normalised’ Colwell P for each site, with negative values broadly signifying potential agronomic response and positive values warranting an assessment of environmental risk. Normalised Colwell P was above zero at approximately half the sites, and &gt;50mgkg–1 at 20% of sites that were considered to present a significant environmental risk, highlighting the need for more effective use of soil testing. Colwell P was highly variable within soil type and land use. No category could be singled out for special attention for management except for dairy and former dairy sites. Where dairy effluent must be applied to soils already high in P, a plan is needed to manage stormwater run-off. Pastures at approximately 20% of sites were ‘degraded’, where the priority should be to improve pasture management and reduce the risk of phosphorus loss in surface erosion.

Physical characterization of a watershed through GIS: a study in the Schmidt stream, Brazil.

Remote sensing and geoprocessing are essential tools for obtaining and maintaining records of human actions on space over the course of time; these tools offer the basis for diagnoses of land use, environmental interference and local development. The Schmidt stream watershed, located in the Sinos River basin, in southern Brazil, has an environmental situation similar to that of the majority of small streams draining rural and urban areas in southern Brazil: agricultural and urbanization practices do not recognize the riparian area and there is removal of original vegetation, disregarding the suitability of land use; removal of wetlands; intensive water use for various activities; and lack of control and monitoring in the discharge of wastewater, among other factors, deteriorate the quality of this important environment.This article aims to achieve a physical characterization of the Schmidt stream watershed (Sinos river basin) identifying elements such as land use and occupation, soil science, geology, climatology, extent and location of watershed, among others, so as to serve as the basis for a tool that helps in the integrated environmental management of watersheds. By applying geographic information system - GIS to the process of obtaining maps of land use and occupation, pedologicaland geological, and using climatological data from the Campo Bom meteorological station, field visit, review of literature and journals, and publicly available data, the physical characterization of the Schmidt stream watershed was performed, with a view to the integrated environmental management of this watershed. Out of the total area of the Schmidt stream watershed (23.92 km(2)), in terms of geology, it was observed that 23.7% consist of colluvial deposits, 22.6% consist of grass facies, and 53.7% consist of Botucatu formation. Major soil types of the watershed: 97.4% Argisols and only 2.6% Planosols. Land use and occupation is characterized by wetland (0.5%), Native Forest (12.83%), Native Forest + Rural Anthropic + Secondary Vegetation + Forestry (43.81%), Urban Anthropic/Urban Area (39.85%), and also Urban Anthropic/Expansion areas (3.01%). Mean annual rainfall is 1337 mm, maximum temperatures range from 10.5°C to 41.6°C and minimum temperatures range from -1.80°C and 26°C, weak winds, occasionally over 5 m/s. Conducting an environmental assessment in this watershed is essential for environmental and land management. However, these assessments are not conducted in all watersheds and, when they are, their frequency is not sufficiency to allow for continuous monitoring, in order to model and predict scenarios, with a view to adopt medium and long-term measures for environmental protection.

GIS methods for sustainable stormwater harvesting and storage using remote sensing for land cover data - location assessment.

Identification of potential sites for rainwater harvesting (RWH) is an important step toward maximizing water availability and land productivity in arid semiarid regions. Characterised as a "water scarce" country, Egypt has limited fresh water supplies, and is expected to suffer from water stress by the year 2030. Therefore, it is important to develop any means available to supply water and maintain human habitability in a sustainable manner. Practiced or simply indispensable in many countries around the world, rainwater harvesting (RWH) promotes a sustainable and efficient manner of exploiting water resources. In the present study, suitable areas for sustainable stormwater harvesting and storage in Egypt were identified using remote sensing for land cover data - location assessment linked to a decision support system (DSS). The DSS took into consideration a combination of thematic layers such as rainfall surplus, slope, potential runoff coefficient (PRC), land cover/use, and soil texture. Taking into account five thematic layers, the spatial extents of RWH suitability areas were identified by an analytical hierarchy process (AHP). The model generated a RWH map with five categories of suitability: excellent, good, moderate, poor and unsuitable. The spatial distribution of these categories in the area investigated was such that 4.8% (47910 km(2)) and 14% (139739 km(2)) of the study area was classified as excellent or good in terms of RWH, respectively, while 30.1% (300439 km(2)), 47.6% (474116 km(2)) and 3.5% (34935 km(2)) of the area were classified as moderate, unsuitable and poor, respectively. Most of the areas with excellent to good suitability had slopes of between 2% and 8% and were intensively cultivated areas. The major soil type in the excellent suitability areas was loam, while rainfall ranged from 100 to 200 mm yr(-1). The use of a number of RWH sites in the excellent areas is recommended to ensure successful implementation of RWH systems.

Deriving World Reference Base Reference Soil Groups from the prospective Global Soil Map product — A case study on major soil types of Africa

The main objectives of the Global Soil Map (GSM) project are the development of high resolution maps for defined soil properties and new digital soil mapping tools. Although many current land use, land capability models and many soil related applications use soil type information, a new global soil type map is not among the objectives of the GSM project. In this presented research legacy data was used to derive centroid values for World Reference Base Reference Soil Groups based on the Global Soil Map project defined soil properties in the specified depth intervals and test the applicability of numerical approaches for classifying soils, based on these specifications. The used variables were strictly following the project definitions such as: organic carbon content, pH, electric conductivity, sand, silt, clay and gravel content, bulk density and effective cation exchange capacity, all calculated for the GSM project defined depth intervals (0–5, 5–15, 15–30, 30–60, 60–100, 100–200cm). No environmental covariates were used in this study. A taxonomic distance and a Random Forest algorithm were tested to derive soil classes with the use of training and validation profiles for accuracy assessment. Results were studied in overall and for each Reference Soil Group. Reasons of misclassifications were identified, along with soil properties, which could increase the accuracy of the tested methods. Although this study did not derive a soil class map, promising results show a possibility to derive a World Reference Base based soil type map from the Global Soil Map product with numerical approaches as long as reliable archive dataset is available as a training population. The Random forest algorithm performed better with 68% classification success compared to the taxonomic distance based results with 47% success for the total number of validation profiles. Classification success differed by Reference Soil Group, those with strict, well defined and easily measureable and/or observable criteria on a certain property (like Arenosols) were classified better with both methods compared to other soil groups with broader definitions (like Cambisols). The study also unfolded completeness and accuracy problems in archive datasets, and the varying accuracy by soil type also revealed soil groups with narrow, precise definitions and groups which may need better definitions in a future global classification system for the better performance of numerical methods.

Observed impact of land uses and soil types on cloud-to-ground lightning in Castilla-Leon (Spain)

The impact of land use on lightning activity has mainly been studied for urban areas; however the number of authors addressing the impact of vegetation on lightning is fairly limited. The relationship of different types of land use and soil (thirteen categories of land use and fourteen major soil types were considered) on cloud-to-ground lightning activity was studied in the Spanish region of Castilla-León from 2000 to 2010. To do this, urban, mining, and industrial areas were found to be associated with enhanced CG-lightning activity. With respect to natural land uses, forest and shrubland were the categories where CG-lightning was seen to be increased. By contrast, non-agricultural vegetated areas and pastures displayed the lowest CG-lightning activity. When the major soil types are considered, rendzinas, podzols, and phaeozems were found to be associated with a slight increase in CG-lightning activity and gleysols and solonchaks seem to decrease it. Assuming there are a plethora of factors which can indirectly affect the charging electromicrophysics and cloud dynamics, the authors provide evidence that soil type shows a significant correlation on CG-lightning flash density and weather characteristics are affected by land uses. It is suggested that the influence of vegetation and soil on surface moisture is one of the main effects contributing to explain the impact of land cover on CG-lightning.

Change in soil organic carbon between 1981 and 2011 in croplands of Heilongjiang Province, northeast China.

Soil organic carbon (SOC) is fundamental for mitigating climate change as well as improving soil fertility. Databases of SOC obtained from soil surveys in 1981 and 2011 were used to assess SOC change (0-20 cm) in croplands of Heilongjiang Province in northeast China. Three counties (Lindian, Hailun and Baoqing) were selected as typical croplands representing major soil types and land use types in the region. The changes in SOC density (SOCD) between 1981 and 2001 were -6.6, -14.7 and 5.7 Mg C ha(-1) in Lindian, Hailun and Baoqing Counties respectively. The total SOC storage (SOCS) changes were estimated to be -11.3, -19.1 and 16.5% of those in 1981 in the respective counties. The results showed 22-550% increases in SOCS in rice (Oryza sativa L.) paddies in the three counties, but 28-33% decreases in dry cropland in Lindian and Hailun Counties. In addition, an increase of 11.4 Mg C ha(-1) in SOCD was observed in state-owned farms (P < 0.05), whereas no significant change was observed in family-owned farms. Soil C:N ratio and initial SOCD related to soil groups were important determinants of SOCD changes. Land use and residue returning greatly affected SOC changes in the study region. To increase the topsoil SOCD, the results suggest the conversion of dry croplands to rice paddies and returning of crop residue to soils.

Analysis of Watershed Attributes for Water Resources Management Using GIS: The Case of Chelekot Micro-Watershed, Tigray, Ethiopia

This study identified the importance of watershed attributes for water resource management using ArcGIS software, ASTER DEM and satellite images for the Chelekot micro-watershed, Tigray, Ethiopia. The study also evaluate the different hydrological parameters which are significant for the water resource management within the micro-watershed and finds the alternative solutions for water harvesting in the study area through the introduction of suitable soil and water conservation structures based on the finding. Principal watershed attributes including drainage pattern, topographic parameters, land use types, and soil types were evaluated and interpreted for the study micro-watershed. ArcGIS software was used for the computation, delineation of the boundary and morphometric analysis of the micro-watershed using topographical maps and ASTER DEM data. Results indicate that the micro-watershed has classified as a dendritic pattern with stream orders ranging from first to fifth order. The micro-watershed has homogeneity in texture and lack of structural control of surface flow. The drainage density is medium which indicates the area contains soils with medium infiltration rates and moderate relief. Drainage texture, stream frequency and the form factor of the micro-watershed are 4.1, 1.7 and 0.4 respectively. The bifurcation ratio of the micro-watershed ranges from 1 to 4.5 and the elongation ratio is 0.7 which reveals that the micro-watershed belongs to the less elongated shaped micro-watershed category. The mean bifurcation ratio of the whole micro-watershed is 3.3 indicating that the drainage pattern is not greatly influenced by geological structures. The micro-watershed land covers includes: cultivated land (75.8%), settlement and open land (10.5%), shrubs and plantation (13.2%), and water body (0.4%). The major soil types are Vertisol (58%), Camisole (32%), Regosol (9.5%) and Luvisol (0.7%). The textural classes are clay (5%), silty clay (22%), clay loam (17%), sandy loam (21%) and loam (35%) based on the soil textural map of the micro-watershed. Our results revealed that using GIS and ASTER DEM data based watershed morphometric analysis and hydrological evaluation at watershed scale is more applied and precise compared to other available techniques.

Carbon dynamics from carbonate dissolution in Australian agricultural soils

Land-use and management practices on limed acidic and carbonate-bearing soils can fundamentally alter carbon (C) dynamics, creating an important feedback to atmospheric carbon dioxide (CO2) concentrations. Transformation of carbonates in such soils and its implication for C sequestration with climate change are largely unknown and there is much speculation about inorganic C sequestration via bicarbonates. Soil carbonate equilibrium is complicated, and all reactants and reaction products need to be accounted for fully to assess whether specific processes lead to a net removal of atmospheric CO2. Data are scarce on the estimates of CaCO3 stocks and the effect of land-use management practices on these stocks, and there is a lack of understanding on the fate of CO2 released from carbonates. We estimated carbonate stocks from four major soil types in Australia (Calcarosols, Vertosols, Kandosols and Chromosols). In &gt;200-mm rainfall zone, which is important for Australian agriculture, the CaCO3-C stocks ranged from 60.7 to 2542 Mt at 0–0.3 m depth (dissolution zone), and from 260 to 15 660 Mt at 0–1.0 m depth. The combined CaCO3-C stocks in Vertosols, Kandosols and Chromosols were about 30% of those in Calcarosols. Total average CaCO3-C stocks in the dissolution zone represented 11–23% of the stocks present at 0–1.0 m depth, across the four soil types. These estimates provide a realistic picture of the current variation of CaCO3-C stocks in Australia while offering a baseline to estimate potential CO2 emission–sequestration through land-use changes for these soil types. In addition, we provide an overview of the uncertainties in accounting for CO2 emission from soil carbonate dissolution and major inorganic C transformations in soils as affected by land-use change and management practices, including liming of acidic soils and its secondary effects on the mobility of dissolved organic C. We also consider impacts of liming on mineralisation of the native soil C, and when these transformations should be considered a net atmospheric CO2 source or sink.

Magnesium balance in four permanent manurial experiments under rainfed agro-ecosystems of India

Magnesium (Mg) plays a vital role in photosynthesis, dry matter production and carbon partitioning in sink organs. Hence, four permanent manurial experiments (20–27 years of duration) under the auspices of All India Coordinated Research Project for Dryland Agriculture (AICRPDA) network centres across diverse agro-ecological regions were carried out to examine the soil exchangeable Mg (ex-Mg), crop uptake and overall Mg balance. Groundnut (peanut), finger millet, rice–lentil sequence and post rainy sorghum were the major crops or cropping systems followed in four permanent manure experiments at Anantapuram, Bengaluru, Varanasi and Solapur, respectively. Nutrient management in all experiments involved control (no addition of nutrients), 100% organic, 100% chemical, and integration of organic and chemical. Except in the finger millet-based system, mean ex-Mg status in the entire profile was higher than the sufficiency level (1.0 cmol(+) kg–1 as a critical limit). Status of ex-Mg (cmol(+) kg–1 soil) in soil profiles was in the order: Solapur (3.80) &gt; Varanasi (2.07) &gt; Anantapuram (1.06) &gt; Bengaluru (0.44). A uniform distribution of ex-Mg was observed in plots that received integrated application of organic and chemical fertilisers. In general, improved status of profile ex-Mg (cmol(+) kg–1) over the control was observed in soils under groundnut (0.19–0.78), finger millet (1.90–3.20), and post rainy sorghum (6.50–7.60, except 4.20 in 100% NPK) cropping. Overall, ex-Mg status and balance of different soil types under diverse crop production systems was influenced by several factors, some of which include soil type with varying mineralogy, particle size distribution, nutrient management strategies and rainfall. Significant positive relationships were observed between ex-Mg status and clay content (R2 = 0.94), soil pH (R2 = 0.92), cation exchange capacity (R2 = 0.98) and mean air temperature (R2 = 0.22), whereas a weak relationship was observed with rainfall (R2 = 0.01). The study gives an account of Mg balance in major Indian soil types and recommends further attention on Mg nutrition in current intensive agriculture.

Radar altimetry backscattering signatures at Ka, Ku, C, and S bands over West Africa

This study presents a comprehensive comparison of radar altimetry signatures at Ka-, Ku-, C-, and S-bands using SARAL, ENVISAT and Jason-2 data over the major bioclimatic zones, soil and vegetation types encountered in West-Africa, with an emphasis on the new information at Ka-band provided by the recently launched SARAL–Altika mission. Spatio-temporal variations of the radar altimetry responses were related to changes in surface roughness, land cover and soil wetness. Analysis of time series of backscattering coefficients along the West African bioclimatic gradient shows that radar echoes at nadir incidence are well correlated to soil moisture in semi-arid savannah environments. Radar altimeters are able to detect the presence of water even under a dense canopy cover at all frequencies. But only measurements at Ka-band are able to penetrate underneath the canopy of non-inundated tropical evergreen forests.

Spaceborne altimetry and scatterometry backscattering signatures at C- and Ku-bands over West Africa

This study presents a comprehensive comparison of radar signatures acquired over West Africa (between latitudes 0°–25°N and longitudes 5°W–25°E) at both C- and Ku-bands using nadir-looking altimeters (35-day orbital period ENVISAT RA-2 over 2003–2010 and 10-day orbital period Jason-2 over mid-2008–2011) and side-looking scatterometers (QuikSCAT over 2003–2009 and ASCAT over mid-2008–2011) that covers the major bioclimatic zones, soil and vegetation types encountered in this region.The backscattering coefficient's time series measured by both radar instruments are generated over regional transects and local sites. Meridian transects from the wet tropics to the arid regions of the Sahara desert demonstrate the spatial and temporal changes of the radar response over the West African bioclimatic gradient in terms of surface roughness, land cover and soil wetness. Nadir-looking altimetry appears more sensitive to variations of surface soil moisture than side-looking scatterometry at both C- and Ku-bands. In contrast, the impact of vegetation on the backscattered signals is found to be lower for nadir-looking instruments compared to side-looking ones.

Responsiveness of Soil Series in Southwestern Nigeria to Single Super Phosphate Fertilization

Application of Single Super Phosphate (SSP) fertilizer in soils with inadequate phosphorus (P) should elicit crop response. However, there is an indication of inconsistent response behaviour to SSP fertilizer in some Nigeria soils despite their low available P. This study identified major soil types in Southwestern Nigeria that are unresponsive to P fertilizer application under screenhouse condition and soil properties that are related to this unresponsive behaviour were determined. Soils from twenty locations in Southwestern Nigeria were selected to evaluate their response to four phosphorus fertilizer rates with a control replicated three times in a factorial arrangement laid out in randomized complete block design. Results indicated that most of the locations responded to initial P application except for Fashola 2 which produced significantly higher maize shoot yield in control soils. There were five other locations where no-response was observed. Multiple regression analysis showed that phosphorus sorption index was related to sand, organic matter and clay. Phosphorus accumulation in soil P reserves may explain the behaviour of the P-unresponsive soils irrespective of their available P levels.